-(void)_test3{

    RACSubject *signalofsignal = [RACSubject subject]; //信号中的信号（也就是发送的数据是信号）

    RACSubject *signal1 = [RACSubject subject];

    RACSubject *signal2 = [RACSubject subject];

    RACSubject *signal3 = [RACSubject subject];

    RACSubject *signal4 = [RACSubject subject];

    //订阅方式1

    //    [signalofsignal subscribeNext:^(id  _Nullable x) {

    //

    //        [x subscribeNext:^(id  _Nullable x) {

    //

    //            NSLog(@"接收信号中的信号的结果%@",x);

    //        }];

    //    }];

    //订阅方式2 (接收到最新的那个信号)

    [signalofsignal.switchToLatest subscribeNext:^(id  _Nullable x) {

        NSLog(@"用 switchToLatest订阅 %@",x);

    }];

    [signalofsignal sendNext:signal1];

    [signalofsignal sendNext:signal2];

    [signalofsignal sendNext:signal3];

    [signalofsignal sendNext:signal4];

    //发送多个信号

    [signal1 sendNext:@""];

    [signal2 sendNext:@""];

    [signal3 sendNext:@""];

    [signal4 sendNext:@""];

}